Oil sands are sand deposits impregnated with a viscous hydrocarbon, bitumen, which occur in various locations throughout the world. One of the largest deposits, and currently the only one being commercially exploited on a large scale, is located in the Athabasca region of the Province of Alberta, Canada. Athabasca oil sands consist of a three component mixture of mineral matter, bitumen and water. The valuable component, bitumen, can range from nearly 0 up to 20 wt% with an average value being about 10 wt%. Connate water typically runs between 3 wt% and 6 wt%. The mineral matter is composed of sands, silts and clays and usually ranges between about 80 wt% and 90 wt% of the deposit. The fines are those mineral materials containing the clays, silts and fine sands which pass through a 325 mesh screen (&lt;44 micron) and are responsible for a great many processing problems. Generally the clay content increases as the oil content or ore grade decreases. For a more complete fines description see R. N. Yong and A. J. Sethi, Mineral Particle Interaction Control of Tar Sand Sludge Stability, The Journal of Canadian Petroleum Technology, Volume 17, Number 4 (October-December 1978).
Currently only the Hot Water process is being used commercially to exploit this resource. This process is well described in the patent and technical literature. In the two commercially operating hot water plants, Syncrude and Suncor, it is the fine mineral matter that is largely responsible for sludge accumulation and tailings disposal problems.
Several solvent extraction processes for the recovery of bitumen from oil sands have been proposed, with the object of overcoming the problems inherent to the hot water process, but to this data no commercially acceptable process has reached fruition. The propensity for fines and other small particles to impede separation of the solids and bitumen solution has been a perennial problem and many techniques to overcome this difficulty have been devised. One technique is to slurry the oil sand in an appropriate solvent after which the mineral matter is classified into a coarse fraction and a fines fraction. By so doing, the fines are removed and treated separately. This is done in order to avoid the problems of blockage in subsequent processing when the coarse mineral matter is washed and the solvent recovered. A typical example of this approach may be found in Canadian Pat. No. 1,169,002 June 12/84 G. B. Karnofsky in which the mineral matter is classified into a major coarse fraction and a minor fines fraction. Solvent is then percolated through beds of the coarse sands to extract bitumen and to wash the sands, while an elaborate series of thickeners, clarifiers and filters are used to treat separately the fines fraction.
Another technique is to add small amounts of water to encapsulate and agglomerate the small particles so that they behave like larger particles which will not migrate through the bed. Thus the addition of a minimal amount of water can improve filtration rates and greatly reduce bed plugging. This method should be effective for Oil Sands containing low and medium amounts of fine mineral matter. An example of this technique, using a high grade (low fines) feed containing more than 10% bitumen, may be found in Canadian Pat. No. 873,852 June 22/71 A. M. Benson in which the filtration rates of the sand solvent mixtures are improved by the addition of water. Up to a total of only 7% water was used to form a "grainy slurry", resulting in an increased filtration rate and elimination of the clay layer usually formed on top of the filter bed.
A method in which fines and sands are separated from the extraction solvent by a spherical agglomeration technique is disclosed in Canadian Pat. No. 1,031,712, May 23, 1978, F. W. Meadus et al. In this process the fines, in conjunction with an aqueous bridging liquid, are utilised to promote binding of the coarse particles into large, dense, compact agglomerates which can be easily separated from the extractant by simple screening. By this means, feed containing high fines are easily handled but a major problem is that feeds with a fines content of less than about 15 wt% are not amenable to this approach due to poor agglomerate strength and must therefore be processed in other ways.